Patent GB-653909-A (GB)
Title: Improvements in or relating to systems and apparatus for conveying information
Inventor: JOHNSON ERIC ARTHUR
IPC: G08C15/04
Filed: 1948-04-28
Abstract: 653,909. Electric followup systems. MINISTER OF SUPPLY. April 28, 1948, No. 11635. [Class 40 (i)] In a follow-up system for reproducing angular position or rotation the transmitter comprises an arm adapted to wipe over a plurality of contact segments ; code signals are transmitted indicative of each segment as it is engaged by the wiper and at the receiver the coded signals are decoded and arranged to position a rotary arm in correspondence with the transmitter. The invention is described as applied to a servo-operated shaft position indicator using coarse and fine controls. The angular positions of both the coarse and fine transmitter rotors are sent in a multidigital code; the code elements are transmitted sequentially or simultaneously, and the receiver fine transmitter is arranged to function only after the coarse receiver has come into alignment. A binary code is preferably used. Fine transmitter, Fig. 1. The input shaft 1 carries wipers 3, 4 movable over commutator segments C1, C2 ... C32, only one wiper being operative at a time. Positive potential is extended from a potentiometer 22, 23 over the operative wiper 3 or 4 and the commutator to a coding unit 110 where the shaft position, i.e. the operative one of the thirty-two segments numbers 1 ... 32 is converted into the binary system giving a five digital number. From the coding unit potential is extended to the appropriate grids of the digital duo-triode amplifiers 11 which operate the associated Eccles-Jordan connected triodes 10, 12 to energize in combination those of the five digital output lines 13-17 appropriate to the shaft position. The sixth digital output line 18 is energized through similarly connected tubes 40, 41 according to the operative wiper 3 or 4, the six-digital coded output thus catering for 64 shaft positions. Coarse transmitter, Fig. 2. The coarse commutator has, as shown, thirty-six segments C1, C2 ... C36, and the shaft 50 is consequently geared to the fine transmitter shaft through a 36 to 1 ratio. Alternatively, the coarse commutator could have thirty-two segments to permit binary system coding. As for the fine transmitter, the commutator segments are connected to a coding unit 110a whereby the operative one of the thirty-six shaft positions results in the energization of the corresponding combination of digital code lines 57 ... 62. The two wipers 52, 53 permit correct co-ordination of the fine and coarse transmitters, the leading wiper engaging a fresh segment as the trailing wiper leaves the preceding segment, this coinciding with the fine transmitter output code passing from 111111 to 000000. Coarse receiver, Fig. 4. The transmitter outputs may be conveyed simultaneously or sequentially over any link and distributed to the appropriate receiver input circuits. As shown, impulses from the coarse transmitter digital lines 57 ... 62, and from the fine transmitter highest digital output line 13 pass over input lines 111 ... 116, and 141, to operate relays 117 ... 122, 143, controlling connections to a decoding unit 110b so arranged that a voltage pattern is set up on the thirty-six commutator contacts which presents zero value on the particular segment corresponding to the digital value transmitted, and voltages increasing positively on one side and negatively on the other side. A voltage of magnitude and sense dependent on the magnitude and sense of the misalignment is thus transmitted over the appropriate wiper pair 134, 135 or 136, 137, a limiter stage 144, and one of the rectifiers 145, 146 to energize a relay 96 or 97, Fig. 3, whereby a fixed positive or negative bias, as the case may be, is applied to the amplifier 93 which drives the output shaft 91 and the commutator shaft 98 through a servomotor 90 in the corrective sense. The relay 117, Fig. 4, operated by line impulses of the highest denomination over line 111 ensures realignment by the shorter route. A further input relay 142 adapted to be energized from line 14 of the fine unit corresponding to “ turn of the fine unit determines which of the two brushes of the pair contacting the small commutator segments determines the coarse "null" position thus setting the shaft to the nearest <SP>1</SP>/ 144  of a turn so that the fine receiver by virtue of the 36: 1 gear ratio will be set within the corect quadrant. When the coarse null position is reached the operative relay 96 or 97 relapses to connect the fine receiver to the servo control. Fine receiver, Fig. 3. The fine transmitter output lines 13 ... 18 are connected respectively over receiver lines 71, 72 ... 76 to relays 82, 81, 83 ... 86. The two highest digital relays 81, 82 control the pattern of the voltage applied to a circular potentiometer 95 from a battery 88, and determine the direction in which the servomotor 90 drives the output shaft, and geared to it the potentiometer arm 94, towards the null position. The potential of the arm 94 is applied over a resistor 100 and contacts of the de-energized relay 97, to bias the amplifier 93 in the appropriate sense to drive the servomotor in the correct direction. The relays 81, 82 thus determine the position of the fine receiver to the nearest “ turn. The lower digital relays 83-86 modify the biassing potential fed from the potentiometer arm 94 to effect the desired fractional turn of the fine receiver arm 94 and hence of the output shaft 91. Modifications. The coarse and fine traiismitters and receivers may be interchanged or used individually.